ᐅ Partition wall thickness in a duplex house. Structural engineer specifies 17.5 cm.

Hello everyone,

We are currently at the early stage of the detailed planning for building our semi-detached house. One of the questions we are facing is whether to use 17.5cm (7 inches) or 24cm (9.5 inches) thick bricks for the party wall between the two units. The structural engineer/architect has currently planned for a thickness of 17.5cm (7 inches).

We are now wondering if the additional 7cm (2.5 inches) would provide significantly better sound insulation, or if we should rather enjoy the extra 7cm (2.5 inches) of internal width.

Our future neighbors in the semi-detached house value good soundproofing, so I assume they will also use at least 17.5cm (7 inches) thickness.

Thank you very much for your help.

What kind of bricks? Structural engineer and 17.5cm (7 inches)... sounds like sand-lime brick...?

Will your neighbor also get 17.5cm (7 inches)? So basically two 17.5cm (7 inches) walls = 35cm (14 inches) total?

I would find just 17.5cm (7 inches) too thin... I would rather go for the 24cm (9.5 inches). Two times 17.5cm (7 inches) seems sufficient to me... at least if it’s sand-lime brick. These are heavy and provide the best sound insulation.

Poroton bricks will be used.

Yes, exactly, the neighbor is also building a wall. However, he will build it later, so we don’t yet know the exact thickness. That means it will be 2x 17.5cm (7 inches) plus the insulation layer in the middle.

kamda schrieb:
Our future semi-detached house neighbor values good sound insulation, so I assume they will use at least 17.5cm (7 inches) wall thickness.

Less is unlikely, and forty years ago, sometimes a shared 24cm (9.5 inches) wall was built.

Sound insulation depends more on the construction method than on wall thickness alone. You cannot think of thickness the same way for building materials as for insulation.

kamda schrieb:
So that means 2x 17.5cm (7 inches) plus the insulation layer in between.

Although that probably refers more to thermal insulation than to soundproofing.

I see no reason to worry that this won't be sufficient.

kamda schrieb:
Yes, exactly, the neighbor is also building another wall. However, they will build later.

That sounds like the neighbor is at least already known. I’ll repeat my usual advice that for semi-detached house projects, it’s beneficial to plan together—that is, to find a shared designer and communicate a bit about each other's plans. The worst situation would be one party building without a basement and the other with one. Open communication brings clarity.

P.S.: Haha, I already mentioned this: https://www.hausbau-forum.de/threads/Doppelhaushälfte-wir-ohne-Keller-Nachbar-mit-Keller.24711
So again, my urgent recommendation: the party building the basement should start first. Or at least both should build simultaneously up to the basement ceiling/floor slab level.

---

https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/

Above all, make sure the second half doesn’t arrive so much later that you still need a protective barrier for your part...

First of all, thank you for your comments. At the moment, we are leaning towards the 17.5 to make use of the approximately 7cm (3 inches) more interior width.

11ant schrieb:

It sounds like the neighbor is at least known already. I’ll repeat my mantra that when building a semi-detached house, it never hurts to plan together, meaning finding a joint planner and exchanging some information about what each party intends to do. The worst scenario would be if the first builder wants no basement and the second builder wants one. Talking brings clarity.

P.S.: Haha, I already said this: https://www.hausbau-forum.de/threads/Doppelhaushälfte-wir-ohne-Keller-Nachbar-mit-Keller.24711
So again, my urgent advice: the one with the basement should build first. Or at least build up to the basement ceiling / slab level simultaneously.

Yes, our neighbor is known and we have already exchanged information. He will also build with a basement. However, he is still in the phase of "collecting offers." We want to start in March (depending on the weather).

Müllerin schrieb:
Above all, watch that the second half doesn’t come much later so that you don’t end up needing a protective wall for your side...

His goal is also to start in 2018. Is it possible to say how much sealing the dividing wall for one winter would roughly cost?